The present invention relates to a mechanical torsional vibration damper.
A problem in automotive engine manufacture is that the torsional vibrations caused by the engine firing order are transmitted from the engine into the drive train, especially when the frequencies come close to the natural frequencies of the system. This is particularly unpleasant at idle speed but also during load reversal situations.
In order to avoid this, various designs of so-called mechanical torsional vibration dampers are known which have elastic damping media in the form of springs or hydraulic components arranged between a primary part connected with the engine crankshaft and a secondary part connected with the clutch.
However, known systems have the disadvantage that they cover only a part of the working spectrum of the drive, but are ineffective in the remaining load range. The problem is that the load range requires a spring force and damping corresponding to the transmitted torque and the speed while at idle speed only minor spring forces and practically no damping is desirable in order to attain declutching at idle. In the critical speed range, i.e. at speeds in the region of the natural frequency, very high damping is required since the circular accelerations would be clearly exceeded compared with the primary side. This speed range is passed especially when starting the engine but also during load reversal situations. At resonance dynamic moments can occur which amount to a multiple of the rated moment.
In this context, reference is also made to commonly assigned copending patent application Ser. No. 08/755,175, now patented entitled Torsional Vibration Damping Assembly, and filed on Nov. 25, 1996, the disclosure of which is incorporated herein by reference. This copending patent application discloses a mechanical torsional vibration damper with a primary and a secondary part which are connected by a positive/non-positive spring and damping system made of tangential compression springs and thrust plungers acting on contact surfaces on the primary and secondary part. This coupling includes a rotating drive disk and a coaxially arranged driven disk rotating in the same direction with means for elastic power transmission wherein the drive disk partly overlaps the driven disk and has radial pockets distributed over the inside circumference of the overlapping part and having a surface area slightly tapering towards its circumferential ends in direction of the drive disk. The surface area of the driven disk has a polygonal cross section, and pairs of wedge-shaped thrust plungers are arranged in the pockets which are kept apart from each other by at least one compression spring. At their sides facing the surface area of the driven disk, the thrust plungers are level or slightly arched, and compression springs are arranged in the drive disk or on the thrust plungers which act on the driven disk and which at idle speed merely exert a resetting moment from the drive to the driven disk but practically no friction force.